As power presses have continued to increase in size and capability, the dies for use in such presses have accordingly increased both in size and weight. Much time and energy, hence cost, must be expended each time these dies are changed. It is, therefore, advantageous to provide mechanically and electrically controlled moving and sliding carriers to facilitate quick die changes.
In the past, bolsters or carriers having sets of wheels driven by hydraulic and pneumatic drive systems have been used extensively in various applications to carry heavy dies. In order to reduce both the amount of downtime for large power presses and the cost of labor of press room workers during changeover from one set of dies to another, manufacturers have long sought to decrease the cycle time of this die changing operation. Also, due to changing economics, modern factories install fewer press lines, which has given rise to frequent die changes for running different parts. It is not uncommon for factories to seek several die changes in a day. In the past, changes were made far less frequently, therefore factories could tolerate fairly long die changing times. Thus, it is now desirable to move the first die carrier out of the press and the second die carrier into the press as quickly as possible.
In moving the carriers into position, various methods have been used to arrest the movement of the carrier once in position. One such method is to install bumpers or stops that stop the movement of the carrier upon impact. Another method has been to cut the motor and allow the carrier to coast to a stop due to the force of friction. Additionally, mechanical brakes have been used to stop the forward movement of the carrier. While each of these methods may stop the motion of the carrier, these methods may be undesirable insofar as each requires a long braking distance or exhibits safety problems due to the inertia of the carrier. As a result, the methods are generally unsatisfactory for providing rapid die changes.